The aim of the proposed work is the development of an advanced implantable rechargeable battery system for the ventricular assist system (VAS). The development of this energy dense system will reduce the size of the necessary power pack or increase the energy contained in the current power pack threefold. This improvement should aid in the performance and patient acceptance of the VAS. High energy density lithium/titanium disulfide rechargeable batteries fabricated with unique high performance cathodes will be studied with three electrolyte systems. The ability of the cells to discharge and charge under current pulses, constant moderate rate and constant high rate will be investigated. Extensive abuse and environmental safety testing will be conducted on the cells to demonstrate the feasibility of their use in an implantable device. The effect of the electrolytes on cell performance and safety will be determined. Additionally, commercial goal of the proposed work is to supply VAS manufacturers with an improved implantable rechargeable power source.